The present invention relates to the recovery of oil and gas from oil-bearing shale and, more particularly, to such recovery by retorting processes wherein crushed raw oil shale is heated to convert the kerogen contained therein to vapor to be recovered by appropriate recovery apparatus.
The basic process employed in the present invention includes combusting organic residue on spent shale to heat the heat-carrying bodies which are recycled to the retort for pyrolysis. A number of other processes include the recycling of spent shale as part of the method of oil shale retorting. The majority of these, however, have not even attempted to keep any portion of the spent shale, such as the finely divided, burned shale ash, from the pyrolysis zone, which has been shown to result in high yield losses in these processes due to adsorption and/or absorption of oil in the process which is subsequently lost to the recovery system. Only the process described in U.S. Pat. No. 3,691,056 to J. H. Barney, et al and assigned to the common assignee of the present invention recognizes this deficiency in processes of the prior art and takes steps to prevent combusted spent shale (i.e., shale ash) from recycling to the pyrolysis vessel. The disadvantage of the process described therein, however, is that it assumes that the recycle of all combusted spent shale should be avoided and, as a result, may require a number of separation and attrition steps to effect the separation of combusted spent shale from the heat-carrying bodies and does not identify and, thus, eliminate those particles which are the major cause of the oil loss.
The method described in U.S. Pat. No. 3,703,442, to R. Rammler, et al., although not directly addressing the problem of oil adsorption on shale ash fines, does take steps to keep the burned fine shale ash from the pyrolysis zone, if only for the purpose of reducing the dust loading in the oil vapors leaving the retort. The process described therein, however, does not include combustion within a dense phase fluidized bed and, as a result, requires separate zones other than the burning zone wherein shale ash fines are sifted with separate propellant gas streams, and neither identifies or takes specific steps to differentiate between the sorption capabilities of the particles and to eliminate the particles primarily responsible for the oil loss.
Further, these prior art workers and others have failed to provide a method for maximum recovery of the sensible heat of the spent shale, choosing instead to rely upon standard coolers for effecting a heat exchange relationship between the hot flue gas/shale ash mixture and a heat exchange medium.
For ease of understanding, the two aforementioned processes and their apparatus as disclosed in the patents are set forth in simplified form in FIGS. 1 and 2 respectively.
In the apparatus of FIG. 1, hot heat-carrying bodies 10 are mixed in a rotary drum retort 18 with crushed raw oil shale 12 from source 14 which has been preheated in preheater 16. As the hot heat-carrying bodies 10 and crushed raw oil shale 12 pass through the retort 18, pyrolysis occurs resulting in vapors 20 and solids blend 22 which enter container 24 from retort 18. Vapors 20 are sent to recovery apparatus 26 where the gas and oil content thereof is removed for commercial exploitation. The solids blend 22 is moved into a combustion vessel 28 having a dense phase fluidized bed combustion zone 30 therein. Larger particles within solids blend 22 are first passed through a crusher 32 where they are reduced in size. As the solids blend 22 passes through the dense phase fluidized bed combustion zone 30, a portion of the shale ash therein is attrited by the scrubbing action of the fluidized bed. Ash, and light particles 34 are drawn off by cyclone 36 and pass through a cooler 38 to a bag filter 39 where they are filtered out and removed as residue 40. The cooled, cleaned air 42 is exhausted. The solids blend 22 having passed vertically through the dense phase fluidized bed combustion zone 30 is drawn off through pipe 44 where it is mixed with hot air 46 from source 48. The hot air 46 and heated solids blend 22 pass into an elutriator 50 containing bars or baffles 52 which are struck by the reheated solids blend 22. As the particles are broken by the bars or baffles 52, the ash and light particles 34 produced continue on through with hot air 46 to join the ash and light particles 34 from cyclone 36 entering cooler 38. The heavier particles rejoin the hot heat-carrying bodies 10 to begin the cycle once again.
Referring now to the prior art apparatus of FIG. 2, crushed raw oil shale 12 is once again supplied from a source 14 to be mixed with hot heat-carrying bodies 10 in a rotary drum retort 18. The vapors 20 leaving retort 18 are passed through multiple stages of cyclones 54 wherein the oil-bearing vapors 20 are passed to recovery apparatus 26 and all other solids, ash, and light particles 34 are passed into the bottom of a stand-pipe 56 having hot air 58 passing vertically therethrough. The output of stand-pipe 56 enters a storage container 11' comprising a tortuous path. The heavier particles forming the heat-carrying bodies 10 are unable to exit storage container 11' through the tortuous path. The hot air 58, ash and light particles 34, enter waste heat boiler 60 where cold air 62 from source 64 is heated to provide hot air 58. The cooled air 66 and particles 34 enter cyclone 68 where the heavier particles contained therein are removed is residue 70. The lighter particles and air are cooled by water 72 and pass into an electrostatic precipitator 74 which separates them into cooled gas effluent 76 and residue 70.
As can be seen, in either of the foregoing prior art techniques, the removal of ash is accomplished by apparatus outside of the primary retorting operation, oil recovery therefrom is not maximized, and maximum energy reacovery is not accomplished.
Wherefore, it is the object of the present invention to provide oil retorting apparatus recycling spent shale capable of overcoming the shortcomings of the prior art oil retorting apparatus wherein oil recovery is maximized and lost energy is minimized.